Fix bugs: reg_value to reg_name, multi_sz decoding

[Ebrix]

Checklist:

• I squashed commits belonging together
• I added unit tests or explained why they are not relevant
  Part of scapy-red
• I executed the regression tests (using tox)
• If the PR is still not finished, please create a Draft Pull Request

During the last PR merge two things were modified and not properly tested: rename of reg_value to reg_name and the decoding of a multi_sz registry type. (scapy-red tests were failing due to those little bugs)

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.28%. Comparing base (3147e10) to head (aa99a49).

Files with missing lines	Patch %	Lines
scapy/layers/windows/registry.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4940      +/-   ##
==========================================
- Coverage   80.28%   80.28%   -0.01%     
==========================================
  Files         375      375              
  Lines       92410    92410              
==========================================
- Hits        74194    74190       -4     
- Misses      18216    18220       +4     

Files with missing lines	Coverage Δ
scapy/layers/windows/registry.py	0.00% <0.00%> (ø)

... and 5 files with indirect coverage changes

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